The present invention relates to a mounting arrangement for a safety switch and a safety switch actuator.
Safety switches are well known, and are typically used to prevent access to, for example, electromechanical machinery when that machinery is in operation. In a conventional arrangement, the safety switch is mounted on a door post of a machinery guard, and an actuator for the safety switch is mounted on a corresponding door. When the door is closed, the actuator engages with the safety switch, which in turn closes a set of electrical contacts which allow power to be supplied to the machinery. This arrangement ensures that power can only be supplied to the machinery when the guard door is shut. When the guard door is opened, the actuator disengages from the safety switch, thereby opening the electrical contacts and cutting off the supply of power to the machinery.
A typical safety switch comprises a housing, in which is provided a set of contacts that are generally fixed in position relative to the housing. An axially slideable plunger is mounted inside the housing, and is moveable relative to the housing. The plunger is provided with another set of contacts. The plunger is biased towards a cam arrangement by a spring. The actuator mentioned above is arranged to engage with the cam arrangement.
In many safety switches, if the actuator is not engaged with the cam arrangement (i.e. if the actuator is not engaged with the safety switch), the cam arrangement is arranged to prevent the contacts on the plunger coming into contact with the contacts of the housing by preventing movement of the plunger (i.e. the plunger is kept in a first plunger position). By preventing the contacts from contacting one another, the switch cannot conduct electricity while the actuator is not engaged with the cam arrangement.
Bringing the actuator into engagement with the cam arrangement causes the cam arrangement to rotate, which in turn causes the plunger (which is biased toward the cam arrangement) to move into a notch provided in the cam arrangement. Such a configuration provides a plunger that is moveable between the first plunger position and a second plunger position. When the plunger moves into the notch, the contacts on the plunger are brought into contact with the contacts of the housing, allowing electricity to flow through the safety switch.
In order to ensure that the actuator is brought into engagement with the cam arrangement, the actuator must be directed through an opening in the housing of the safety switch. If for some reason the actuator is misaligned with the opening, when the door to the machinery guard is closed the actuator may not pass through the opening in the housing, but hit the housing. If the actuator hits the housing, one or both of the housing and the actuator may become damaged. Alignment of the actuator with respect to the opening of the housing can be made even more difficult if the door post to which the safety switch is mounted is vibrating, or if the door to which the actuator is mounted is vibrating. Misalignment of the actuator with the opening in the housing may also occur due to wear and tear of the door of the machinery guard. For example, the weight of the door to the machinery guard may cause the door to, over time, move in a vertical direction causing misalignment of the actuator relative to the opening in the housing.
Even when the actuator is satisfactorily aligned with the opening of the housing, and the actuator is brought into engagement with the cam arrangement of the safety switch, problems can still be encountered. Problems can occur if there is relative movement between the door to which the actuator is mounted and the door post to which the safety switch is mounted. For example, if the door moves vertically relative to the safety switch, the actuator may become bent, and/or the safety switch may be damaged or removed from the door post. In another example, if the door moves away from the door post due to vibrations caused by operating machinery, the actuator may be disengaged from the cam arrangement of the safety switch. Disengagement of the actuator from the safety switch causes the safety switch to turn off the supply of power to the machinery within the machinery guard. It is possible that, due to vibrations, this process of cutting off the supply of power to the machinery may be repetitious, i.e. following the cycle of the vibrations (e.g. the power supply to the machinery may ‘flutter’). Even if the supply of power to the machinery is not interrupted, the movement of the actuator may cause wear on the cam arrangement, and other parts of the safety switch.
It is therefore desired to provide a reliable safety switch mechanism that has generally repeatable operating conditions and which overcomes one or more of these or other disadvantages.